A long-held belief that women are moody in the days before their period is largely a myth, according to a New Zealand researcher.

Drawing on 41 studies dating from 1971 to 2007, Dr Sarah Romans and colleagues at the University of Toronto found little evidence to support the theory that there is a link between mood and the pre-menstrual phase.

Just 15 per cent of the studies reported negative mood in this phase while 38 per cent found no link at all. Another 38 per cent of the studies found there was a link during the pre-menstrual phase but also during the menstrual phase. And in 9 per cent of studies, women had negative moods at a time unconnected to their period.

"A very small proportion found a pre-menstrual dip in mood, most of them found no link between women's depression and anxiety and their menstrual cycle."

Dr Romans said attributing women's emotions to their reproduction was "deeply embedded" in many cultures."There is this troublesome tendency that if a woman is distressed, anxious or depressed to automatically think there's a hormonal explanation for it, not to think it might be something happening in her life such as her work or home life.

"I'm certain there are [other explanations] to do with social processes, inter-personal processes, social support, her physical health, how much recognition she's getting for what she's accomplishing, what's going on in her key relationships."

To support this, researchers also asked 500 women what factors influenced their moods.

"We didn't prompt them to mention menstrual cycle or reproduction and under 2 per cent volunteered that explanation."

In another study, women were misled about the date their period was due to start, resulting in more symptoms being reported at that time - further proof that it's not necessarily biological factors at work, she said.

"What we're trying to tease apart is how much comes from the biology of reproduction and how much more comes from external things happening in a woman's life."

Dr Romans emphasised that the literature review did not look at premenstrual dysphoric disorder. .

Dr Romans, who spent eight years in Canada, has since moved to the University of Otago where she is a professor of psychological medicine.

Nutritionist and author Libby Weaver said in her experience of dealing with clients with PMS, which is also referred to as premenstrual tension (PMT), their symptoms were very real.

"A woman doesn't just dream up impatience, feelings of anxiety and swollen, heavy, tender breasts, and clots the size of golf balls that come out of them. They don't make that up.

Dr Weaver said women with PMS tended to have higher levels of oestrogen leading into their periods and lower levels of progesterone than was ideal.

What is PMS?*

* About 90 per cent of women get advance warning of an approaching period with physical and/or psychological changes.* Symptoms are often mild but about a third of women say PMS significantly affects their life, with 5 to 10 per cent classifying their PMS as severe.* There are more than 100 recognised symptoms that may be due to PMS.* These include: irritability; mood swings; poor concentration; tiredness; swelling and bloating; headaches; breast tenderness.*Source: Netdoctor.co.uk

However ...

* 38 per cent of research studied by Dr Sarah Romans reported no link between negative mood and the pre-menstrual phase.* 38 per cent found that mood was low but it was not specific to the pre-menstrual phase.* 15 per cent reported negative mood in pre-menstrual phase.* 9 per cent reported negative moods unconnected to periods.